Scientific Concepts: Theory and Practical Application
What the exam expects
Scientific Concepts questions test whether you can connect basic science to what happens at the shampoo bowl and the chemical station. Know the pH scale (0–14, 7 neutral): hair and skin prefer mildly acidic to neutral products, and the pH of a solution drives how much the cuticle lifts. Understand keratin as the protein building block of hair, held together by disulfide bonds (broken by relaxers and perms), salt bonds (broken by pH change), and hydrogen bonds (broken by water, reset by heat and rollers). Know the three layers - cuticle (protective, scales), cortex (bulk, pigment, strength), medulla (central core, not always present).
Anatomy and chemistry links
Be ready for skin and hair growth cycles (anagen, catagen, telogen), the structure of the hair follicle and sebaceous gland, and the difference between eumelanin (brown-black) and pheomelanin (red-yellow) pigments. In chemistry, know the difference between suspensions, solutions, and emulsions, and recognize that water is the universal solvent while surfactants allow oil and water to mix.
Traps candidates fall for
- Confusing the cortex (where color and bonds live) with the cuticle (where lifting begins).
- Assuming a higher pH is always stronger - high pH swells and roughens hair; low pH smooths it.
- Mixing up electrical and chemical effects: galvanic, faradic, and cataphoric currents belong to electrotherapy, not to perms.
Rule of thumb
Match the science to the service: if the service breaks a bond, name the bond and name what rebuilds it. Disulfide bonds broken by a relaxer are rebuilt in the neutralization step - that one sentence answers many questions.
Worked example
A client's hair feels rough after a high-pH shampoo. Reasoning: high pH lifts the cuticle, increasing friction. The corrective is an acidic conditioner that closes the cuticle - not a stronger shampoo.